Fine and coarse signal mixing circuit



Aug. 13, Y1963 I J. BENTKowsKY 3,100,859'

FINE AND coARsE SIGNAL MIXING cIRcUII Filed Nay 29, 1961 FIC-3.1.

INVENTOR.

ATTORNEY l 3,100,859 l FINE AND CGARSE SIGNAL MHXING CIRCUET Jerome Bentkowsky, Charlottesville, Va., assigner to Sperry Rand Corporation, Great Neck, NX., a corporation -of Delaware Filed May 29, 1961,v Ser. No. 113,418 5 Claims. (Cl. S18- 30) This invention relates to signal mixing circuits and in particular to signal mixing circuits especially adapted for use in -a servo system wherein fine and coarse error signals are employed in the control of a servomotor.

More particularly, the present invention relates to servo systems in which a ine and coarse signal voltage mixing circuit is provided having an output lfor accurately controlling the servomotor with respect to a controlling device, the mixing circuit including means for effectively transferring control of the output from the tine input to the coarse input when a disagreement exceeding a predetermined amount exists between the position of the controlled object driven by the servomotor and the position of the controlling device.

The present invention is an improvement over the apparatus shown in U.S. Patent 2,614,237, is-sued October 14, 1952, to R. `C.'Goertz, entitled Signal Mixing Circuits. In a system of the type shown in the aforementioned U.S. patent, the circuit exhibits ra very high signal United States Patent C gradient for small signals (essentially the ygradient of the 'signal fromthe tine or high speed synchro) and a lower gradient for large .signals (essentially the kgradient of the signal from the coarse or low speed synchro). While this output signalis satisfactory -for certain types of positionalservo systems, vthere are Iapplications where greater accuracy `is required. Particularly for computation purposes, the outputmust essentially resemble the signal from the low Aspeed synchro. In applications of this type, it is also highly desirable that the output signal be linea-r and that the transition trom one type ofy input signal to 'another be accomplished smoothly. Further, itis desirable that the circuit which accomplishes this Iresult be as simple and reliable as possible and of the type which does not require that its characteristics be-precisely matched lto the characteristics of other portions ot the circuits. v t

It is -a primary object ofthe present invention to provide an electrical circuit :for producing an output voltage primarily resembling one input signal While retaining the beneficial characteristics `of another input signal.

It is another object of the present invention to pro- Vide ari-electrical circuit for mixing dual speed synchro signals to provide an output Voltage primarily resembling the coarse or low speed signal While retaining the accuracy and nul-l characteristics of the line or high speed signal.

'It is an additional object of the present invention to provide an electrical circuitv :for mixing dual speed synchro signals Where labove a `predetermined value one of saidsignalsi-s provided Ias an output signal `and below said` predetermined value the more -accurate'signal is used solely.

ice

2 nal is below the predetermined value, the coarse signal is blocked and the output from the second circuit is representative of the tine signal, When the coarse signal is above the predeterminedvalue, the coarse signal circuit is effective in the feedback loop of the second circuit to eiiectively attenuate the, tine signal in order that the output signal is the resultant of the coarse and fine' signals and incorporates the beneficial .characteristics of both. 0 l

Referring now to the drawings, Y

FIG. 1 is a schematic diagram of la servo system embodying the dual speed mixing circuit of the present invention; and l FlG. 2 is a graph illustrating the relationship between the line and coarse input signals land the output signal.

The invention will now be described with respect to a positionable control system, for purposes of simplicity, it

being appreciated however that the invention is equally applicable and particularly advantageous where the output signal is utilized for computation purposes.

Referring now to FIG. l, iine and coarse signals are produced in response to angular displacements of a controlling device ltl which is connected to cause rotation of a shaft 11. Rotatable with the shaft 11 is a rotor l2 which is energized by an alternating current source 13 .thereby inducing in a'transmitter 14 `an electromagnetic iield which will assume a position dependent upon the angular position oi the-rotor 12. This electromagnetic held is reproduced in direction in a receiver unit 16 which islocated at some position remote from the transmitter unit 14 and connected thereto by means of leads 1S. A rotor 17 is arranged to'rotate Within the eld of the stator of the receiver unit lo and is positioned in an angular sense by a motor 18 in yaccordance with the position of its motor shaft 19 `as transmitted through shafts Ztl and 21 and associated gearing. A controlled object 22 is simultaneously driven by the .motor 18 throughits shaft 19. o l

As the purpose of the entire system is to energize the motor 1S to drive its shaft 19 in positional agreement with t-he controlling device 1t), upon the occurrence of a disagreement between the angular position of the shaft -19 and the angular position of the shaft 11, Ia corresponding `angular discrepancy will be evidenced between the rotor 17 which was positioned Iby the motor 1S land the rotor 12 which was positioned by the controlling device 10. Since the angular position of the rotor 12 is transmitted to the receiver 16, any disagreement between the rotor 17 and the positionof the field created by the receiver 16 will serve to create an output signal or voltage, Vc, from the rotor 17 that is dependent in amplitude and phase upon the extent yand directionA respectively The above objects are`=accomplished by the present invention in which, for example, coarse and fine synchro signals are connected to first 'and second circuits respectively. The lirst circuit includes blocking means -for blocking the voltage suppliedthereto below a predetermined value and thekrst circuit -form-s a feedback loop of the second circuit. The output signal from thesecond circuit is then dependent upon the .predetermined value of the coarse signal. When'the value of the coarse signer.

signal is substantially the same as that for producing the` of the disagreement between the controlling device lil |and the controlled object 22 which signal is known-as the coarse or low speed error or input signal.

in order to provide greater sensitivity, i.e., closer synchronization in the region of small angular disagreements between the position of the controlled object 22 -with respect to the controlling device 10, a line or high speed error or input signal is produced in a conventional man- The electrical circuit for producingthe fine error coarse error signal and includes a rotor 26, transmitter Z7, transmission lines 23 and Ia receiver unit 219 including a rotor 31. The line error signal or voltage, VF, appears at the output of the rotor 3.1. Rotation of the controlling device 10 produces rotation of the rotor 26 byimeans of a gear train 34; the gear train 34 produces a rotation of therotor 26 which yisa given multiple N of the rotaf tion of the input shaft v1.1, for example 36:1. ln order rotors 1,2 and 26, both of the error signals Will be of the same frequency but due tothe ratio of angular displacement of the fine error signal generator as compared to the coarse error signal generator, the cycle of the envelope of the fine error signal u/ill bear aratio of N:l to the cycle of the envelope ofthe coarse error signal.

'For small values of actual error, it is desirable to block the coarse error signal from controlling the servomotor 18 since the fine error signal positions the controlled object 22 with respect to the controlling device 1li more v accurately with respect to a null condition then 'the coarse error signal. This value may for example be approximately 22 of error. iIn order to have the output signal which energizes kthe motor l18 resemble the fine error signal IWithin this range while retaining the accuracy and null characteristics of the fine error signal above this Value the dual speed synchro mixing circuit of the present invention 'Will now be described.

The rotor 31 is connected through a balancing resistor 40 to an input terminal of an algebraic summing amplifier 441 which in turn has its output terminal connected to the motor `18. The output terminal is also connected in feedback fashion through la feedback resistor 42 to an input terminal of the amplier 41.

The rotor 17 is connected through a balancing resistor 43 to an input terminal of a summing amplifier 44 which in turn is connected through a blocking circuit 45 to another input lterminal of the amplifier 41. The output terminal of the 'amplifier 41 is connected in feedback fashion through a feedback resistor 46 to an input terminal of the amplifier 44. The blocking circuit 45 may comprise a pair of oppositely poled diodes 'Sil and 51 which are self biased to block the voltage supplied thereto below a predetermined value and to permit the passage of signals above said predetermined value. Alternatively, the diodes 50 and 51 may be biased from a voltage source as disclosed in the aforementioned U.S. Patent 2,614,237.

ln operation, for small discrepancies in the angular relationshipof the shaft 1.1 'with respect to the shaft 19y of less than 2 for example, the coarse error signal is less than the predetermined value and the blocking circuit 45 acts'as :an open circuit. The fine error signal is amplified in the amplifier 41 to energize the motor 18 to accurately position the shaft 1,9 in a direction and in ank amount to eliminate the fine error signal.

For large angular discrepancies where the coarse error signalV exceeds the value representative of i2", the blocking circuit 4-5 acts as a closed circuit and the impedance thereof is negligible. This in effect places the coarse error signal circuit consisting of the coarse error signal from the rotor 17, the resistor 43, the amplifier 44, the blocking circuit 45 and the resistor 46 in the feedback path of thefine error signal circuit consisting of the fine error signal from the rotor 3l, the resistor 40, the amplifier 41 rand the resistor `42. The effect of this is to attenuate the fine error signal because of the high gain of the coarse error circuit being applied in the feedback path of the fine error signal circuit. Further, the output "of the amplifier 41 is linear and the transition from one error input signal to another is accomplished smoothly with the output yof the amplifier 41 being the resultant of the fine and coarse error signals such that the output signal resembles the coarse 'error signal while retaining the accuracy and null characteristics of the fine error signal. When the coarse error signal is less than the predetermined value,the output Voltage from the aml plifier `41 into the motor .18, where V0 is the equivalent to the output voltage, is: R2 A1 il nl 1+i-11 VF Where A1 is the gain of the amplifier 41.

If A1 is large, then Vo I RIVE Y Within the linear region of the fine error signal VF=NV Y so that l a Vo-NRIVC With the coarse error signal exceeding the Vpredetermined value, the output voltage from the amplifier 41 is n A1f12].R1r A1 1V fla 1+A1A2 CTR2+A2RiL1+A1A2 F Where A2 is the gain of the amplifier 44.

-If A1 :and A2 are l-arge, then t Vo-RSVG na2 Ra- R1 then the output of the amplifier 41 will be linear, that is the transition from high to low speed synchro operation Will be made smoothly. Suitable values have been found to be as follows: Y

' vention. The coarse error signal Vc appears at A. r[he fine error signal appears at B. The fine error signal is attenuated so that its gradient near null is the same as that of the coarse error signal." The resultant output signal from the circuit appears at C.

While the invention has been described with respect to a blocking circuit 45 comprising oppositely poled diodes 50 and 51 it will be appreciated that any suitable type of v blocking circuit adapted to block a signal below a predetermined value is acceptable.

yWhile the invention has been described in its preferred embodiment, it is to be understood that the words which have been used are vvords of description rather than of limitation and that changes within the punview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

What is claimed is: n

l. IIn a control system having a controlled object and a controlling object, high speed land low speed transmitters operated from said controlling object, high speed and low speed receivers electrically connected to said high and low speed transmitters respectively and mechanically connected to said-r controlled object for providing high and low speed signals respectively, a first circuit responsive to said low speed signal, said first circuit including blocking means for blocking the voltage supplied thereto below a predetermined value, and a second circuit responsive 'to said high speed signal, said first circuit forming a feedback loop of said second circuit when said low speed signal is above said predetermined value whereby for low speed signals below said predetermined value said blocking means is effectively an open circuit and for 'low speed signals above said predetermined value said blocking circuit is effectively closed, in the latter case said high speed signal is eifectively attenuated due to the high gain of said low speed signal in the feedback path of the high speed signal circuit :and thus thek transition from p one speed signal to another is accomplished smoothly.

' 2. In a control system having ya controlled object and cluding `firstamplifyingmeans 'andblockingl means for f Vblocking the voltagev supplied thereto below' a predetermined value, and :a second circuit including second am- A plifying means responsive to said high speed signal, saidv tirst circuit forming a feedback loop of said second circuit when said low speed signal is above said predetermined value whereby for low speed signals below said predetermined value said blocking means is effectively an open circuit and for low speed signals above said predetermined value said blocking circuit is eiectively closed, in the latter case said highl speed signal is effectively attenuated due to the high gain of said low speed signal in the feedback path of the high speed signal circuit and thusV the transition from one speed signal to another is accomplished smoothly.

3. vIn a system for mixing two voltages, first signalY geny Vbelow 'said predetermined .value said rst signal is eiective and above said predetermined val-ue said second v` Ysignal Vis eiective and smooth transition from one effec-- blocking the voltage supplied thereto below a predefmined value, means connecting said blocking means between an output connection of said second amplifying `means` and an input connection of said first amplifying means, and means .connecting tan `,output connectionl of said iirst'amplifying means in feedback V'fashion to`an in-A put connection ofsaid second amplifying means whereby tive `signal to another is accomplished.

4. In a system as claimed in claim 3^ wherein said l blocking means includes a pair of diodes having a xed enating means for providing a yfirstv signal, second Vsignal generating means for providing a second signal, firsts summing and amplifying'means responsive to said rst signal 5. In va system for mixing wiine and coarse signal voltages, iine signal transmission means for providing a tine signal, coarse signal transmission means for providing a coarse signal, lrst algebraic summing and amplifying means having an input terminal connected to be responsive to said line signal and an output terminal, a flirst feedback connection connecting said output terminal to an input terminal of said iirst amplifying means, second amplifying means having an input terminal connectedk to be responsive to said coarse signal and an output terminal, blocking means connected between the output terminal of said second amplifying means and an input terminal of said iirst amplifying means for blocking voltage supplied thereto below a predetermined value, and means connecting the-,output terminal of said first amplifying means in feedback fashion to an input terminal of said second amplifying means. l

References Cited in the file of this patent UNITED STATES PATENTS 2,560,337 Fouassin July l0, 1951 

1. IN A CONTROL SYSTEM HAVING A CONTROLLED OBJECT AND A CONTROLLING OBJECT, HIGH SPEED AND LOW SPEED TRANSMITTERS OPERATED FROM SAID CONTROLLING OBJECT, HIGH SPEED AND LOW SPEED RECEIVERS ELECTRICALLY CONNECTED TO SAID HIGH AND LOW SPEED TRANSMITTERS RESPECTIVELY AND MECHANICALLY CONNECTED TO SAID CONTROLLED OBJECT FOR PROVIDING HIGH AND LOW SPEED SIGNALS RESPECTIVELY, A FIRST CIRCUIT RESPONSIVE TO SAID LOW SPEED SIGNAL, AND FIRST CIRCUIT INCLUDING BLOCKING MEANS FOR BLOCKING THE VOLTAGE SUPPLIED THERETO BELOW A PREDETERMINED VALUE, AND A SECOND CIRCUIT RESPONSIVE TO SAID HIGH SPEED SIGNAL, SAID FIRST CIRCUIT FORMING A FEEDBACK LOOP OF SAID SECOND CIRCUIT WHEN SAID LOW SPEED SIGNAL IS ABOVE SAID PREDETERMINED VALUE WHEREBY FOR LOW SPEED SIGNALS BELOW SAID PREDETERMINED VALUE SAID BLOCKING MEANS IS EFFECTIVELY AN OPEN CIRCUIT AND FOR LOW SPEED SIGNALS ABOVE SAID PREDETERMINED VALUE SAID BLOCKING CIRCUIT IS EFFECTIVELY CLOSED, IN THE LATTER CASE SAID HIGH SPEED SIGNAL IS EFFECTIVELY ATTENUATED DUE TO THE HIGH GAIN OF SAID LOW SPEED SIGNAL IN THE FEEDBACK PATH OF THE HIGH SPEED SIGNAL CIRCUIT AND THUS THE TRANSITION FROM ONE SPEED SIGNAL TO ANOTHER IS ACCOMPLISHED SMOOTHLY. 